Structural Engineers Association Head Reveals 4 Causes Behind Sai Fai Intersection Road Collapse, Points to Loss of Soil Base Support

At 4 p.m. on May 9, 2025, Bangkok Deputy Governor Vishnu Saipharunpol and Department of Public Works officials inspected the site of the road collapse occurring during construction of a drainage system and siphon pipe for the Sai Fai intersection underpass project. The contractor, Kamphaengphet Vivattana Construction Company Limited, is investigating the cause of the 5-meter stretch of severe subsidence that injured one motorcycle rider.

Prof. Dr. Amorn Pimmanmas, chairman of the Structural Engineers Association of Thailand and faculty member of the engineering department, analyzed photos showing subsidence in a single lane with the road cracking in a V-shape. This indicates loss of soil base support rather than surface pavement damage. He identified four possible causes: 1) Underground pipes or utility vaults such as electrical conduit junction boxes may have leaked at connection points, allowing soil to flow into the vaults; 2) recent rainfall may have softened the soil, making it more susceptible to flow; 3) nearby construction work involving excavation or ground exposure could allow soil movement; and 4) broken water or drainage pipes allowing water to wash away soil.

Relevant agencies must inspect underground utilities in the area. While this collapse appears less severe than the recent Vajira Hospital road collapse, which occurred near the underground railway construction, authorities should monitor for further expansion, particularly during rainy seasons when saturated soil flows more easily. Officials should use underground scanning equipment to check for cavities at regular intervals, as even small voids can pose hazards to drivers.